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Pier height for automated ROR? 50"?

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#1 Footbag

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Posted 05 February 2013 - 09:35 AM

I'm trying to determine my pier height for a ROR observatory I'm building. It is tighter for space then many other observatories I've been looking at, but it's for 99% imaging and will be setup for remote access. It will likely be 11'x7' with a 4'x7' warm room on one end. The wall height will be 76" or 6'4". The interior observatory itself will be 7'x7'.

So I put my AP Mach 1 in Park 1 with my largest OTA(Edge 800), and the highest point of it is 18" over the pier top. I definitely want to leave enough space in case I get a new mount or OTA in the future. I'm going to leave some extra space in for future proofing.

Here's where I'm confused... If I take the wall height (76") and subtract the pier to OTA height (18")I get a pier height of 58". I figure that future proofing it would bring it down into the 52" height range or even 50" and consider using an AP 8" extension of necessary. But does that sound high? I feel like it's higher then most I've seen. In fact, many piers I've seen don't seem to allow the mount to view Polaris. IS this just personal preference, or is there a concern with having a pier or OTA too high? OR is the bigger concern having it too low? Once again, it's for imaging so maybe that changes my requirements.

Also, is assuming it will be parked in park 1 before the roof is closed god practice?

#2 rimcrazy

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Posted 05 February 2013 - 10:24 AM

For quality imaging you don't want to shoot much less than 30 degrees above the horizon so figure the height of pier that will allow you to get, say down to 25 degrees up for a little head room and go with that. It's a fairly simple trig problem.

#3 Madratter

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Posted 05 February 2013 - 10:30 AM

I can also tell you I wish I had built my roll off roof with higher walls so that I could have used a standard door (80" not counting the frame). You are close to high enough. Are you sure you don't want to add a couple more inches?

#4 Alex McConahay

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Posted 05 February 2013 - 11:52 AM

There is a calculator on the AP website that allows you to throw in all the factors (tube diameter, pier height, mount height, wall height, distance from walls, wall height, ........) and make the calculations.

Alex
Below is the result of my calculations on that spreadsheet.

H Wall 78 Height of wall Fixed
D Wall 56 Distance to wall Fixed
A elevation 20 Desired lowest angle of Observing/Imaging (in degrees) Variable at builders desire
H Concrete Pier 34 Height of Concrete Fixed
H Bolts 1 Height of Pier-Stub base plate above Concrete Variable depends on nut placement on foundation bolts (bolts come 3 inches above concrete)
H Mount 12.5 Height of Mount (BasePlate to center Dec Axis)-- Fixed. Result of calculation (Dimension G) in AP spreadsheet for 34 degrees, with dec axis in Park 1.
H Stub 21.0 Height of Pier-Stub Formula: H Stub=Hscope- H (concrete, Bolts, Mount)

Radians 0.34906585 A Elevation converted to Radians For Calculations
Tan (A elevation) 0.363970234 Tangent of A elevation For Calculations

H elevation 20.4 Height from RA/DEC center to top of Wall Formula H elevation=Tan(A elevation)* D Wall
Hscope 57.6 Height of RA/DEC center above floor Formula H scope=H wall-H elevation

NOTE: Given an 18 inch OD tube, and zero clearance for roof, maximum height H Scope in Park Position 1 is 69 inches. This uses a pier stub of 21 inches (approx).
This calculation is for scope in Park 1, which gives lowest view for due south. IS THIS TRUE?????
This calculates for optical axis. Half the tube is below the axis, and therefore has shadow of wall. IS THIS TRUE??? Does it matter?
Based on formula from Mike Dodd, (mike@mdodd.com, astronomy.mdodd.comm)

#5 Lorence

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Posted 05 February 2013 - 03:33 PM

Also, is assuming it will be parked in park 1 before the roof is closed god practice?


One of the biggest concerns I had when designing my observatory was the possibility of the roof colliding with the telescope. One can design a fail safe to prevent this from happening under normal use but in the case of a remote controlled observatory something can go wrong. The telescope may not be able to be parked or the fail safe could fail. You could be in a situation where the roof will not close.

My roof can be closed at any time and I could still do it with a telescope twice the size of the one I have now.

As for wall height, you have to decide how far down to the horizon you want to be able to view and how much protection you want from the wind. It's easy to set up your telescope on a tripod and mock up the walls around it. A few feet of floor space, a tape measure and some masking tape is all you need.

#6 Footbag

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Posted 06 February 2013 - 01:48 PM

OK. I posted this question when I had my telescope and mount setup in kitchen. I was taking measurements so I could figure out the height of my pier, walls, etc...

Well, I discovered Google sketchup. What an awesome program. I've been looking for something like it for a while. So I spent the last 24 hours learning and using it.

I designed and redesigned the observatory three separate times. Then I was actually able to walk around it and see what I liked and didn't like. I'm planning to redesign one more time, with actual specs; but I figured I might as well measure one more time when I can get up to the site to measure.

Just using sketchup has convinced me to raise the wall height to 78". I'm still thinking I like the higher pier, so 50 inches is a possibility.

I'm not sure if the link will work, but here's the preliminary design.

http://sketchup.goog...9ede2910c7e9...

#7 Raginar

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Posted 06 February 2013 - 03:01 PM

I agree with Lorence, I've run my roof into my scope (with no real damage mind you, it's more just a "Why won't the roof move, oh darn!") It also is annoying to 'home' the scope after every run.

#8 Footbag

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Posted 06 February 2013 - 03:14 PM

Interesting, I was just getting used to the idea of having the scope extend well out of the observatory, and then park it when it's time to sleep. I know the auto roof closer can detect if something is blocking the beam. I figured that as long as I remember to use the remote closer, it would have a fail-safe.

I'm really trying to maintain as much southern exposure as possible, so I like the idea of the scope extending high up.

Now, I'm going to try and figure out my footing locations and get them up to local code.

What I really want to do is go up to the site and start digging holes. I figure that if I start digging and don't get stuck, then I could probably do the project myself.

If I start digging and I get tired and then my back goes out, then it will be a sign that I should hire someone.

#9 Madratter

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Posted 06 February 2013 - 03:20 PM

Consider a suggestion that was made to me. Depending on what direction is South in your drawing, it might be possible to have part of that South wall fold down. And if you are already at 78", are you sure you don't want to go another 2" to allow standard size doors?

#10 Footbag

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Posted 06 February 2013 - 03:31 PM

Consider a suggestion that was made to me. Depending on what direction is South in your drawing, it might be possible to have part of that South wall fold down. And if you are already at 78", are you sure you don't want to go another 2" to allow standard size doors?


South is the direction the roof opens. That is why the roof has the flat top, but when I'm at the site, I'm going to figure out exactly what angles I'll need. But I don't think a drop down wall would help.

As far as wall height, I was surprised that the suggestion was to raise it. Originally, it was going to be 74", I'm 73.3/4". Then I raised it up so I could fit through the doorway. Maybe I'll consider raising them some more. It would be nice to use a standard door size.

The rendering is giving me confidence to do things I couldn't visualize otherwise.

#11 Raginar

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Posted 07 February 2013 - 01:27 AM

Adam,

You thought about having your roof roll North? Then you could do a drop down. Just an idea :).

#12 Footbag

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Posted 07 February 2013 - 09:22 AM

Adam,

You thought about having your roof roll North? Then you could do a drop down. Just an idea :).


I would love it if it could, but this structure is going to be up against a house and a north rolling roof and it's supports would obscure the view.

#13 Madratter

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Posted 07 February 2013 - 10:19 AM

The view you have is the view you have. But in my opinion the Southern view is by far the most important. If you can move the observatory to get that view, it would be good to do so.

That said, I spent the solid majority of my time last night looking to the North.

#14 Footbag

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Posted 07 February 2013 - 10:25 AM

The view you have is the view you have. But in my opinion the Southern view is by far the most important. If you can move the observatory to get that view, it would be good to do so.

That said, I spent the solid majority of my time last night looking to the North.


The location I chose is the absolute best on the entire property for southern view. The only other things I can do is keep the pier as high as possible and give the roof a small pitch.






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